Data from: Ecological segregation in a small mammal hybrid zone: habitat-specific mating opportunities and selection against hybrids restrict gene flow on a fine spatial scale

The degree to which closely related species interbreed is determined by a complex interaction of ecological, behavioral, and genetic factors. We examine the degree of interbreeding between two woodrat species, Neotoma bryanti and N. lepida, at a sharp ecological transition. We identify the ecological association of each genotypic class, assess the opportunity for mating between these groups, and test whether they have similar patterns of year-to-year persistence on our study site. We find that 13% of individuals have a hybrid signature but that the two parental populations and backcrosses are highly segregated by habitat type and use. Also, we find that adult hybrids are comparable to parental types in terms of year-to-year persistence on our site but that, among juveniles, significantly fewer hybrids reach adulthood on site compared to their purebred counterparts. Our analyses show that this hybrid zone is maintained by occasional nonassortative mating coupled with hybrid fertility, but that these factors are balanced by lower apparent survival of juvenile hybrids and habitat-based preference or selection that limits heterospecific mating while promoting backcrossing to habitat-specific genotypes. This system presents a novel example of the role that sharp resource gradients play in reproductive isolation and the potential for genetic introgression.

近缘物种间的杂交程度，由生态、行为与遗传因素的复杂交互作用共同决定。本研究聚焦于两种林鼠（Neotoma bryanti与N. lepida）在急剧生态过渡带中的杂交程度。我们将识别各基因型类群的生态关联，评估类群间的交配机会，并检验这些类群在研究样地的年际存续模式是否一致。研究发现，13%的个体具有杂交特征，但两个亲本种群与回交个体的分布高度依赖生境类型与利用方式而彼此分隔。此外，本研究观察到，成年杂交个体在样地的年际存续率与亲本类群并无显著差异，但在幼体阶段，相较于纯种个体，仅有极少数杂交幼体能顺利成长至成年。分析结果表明，该杂交带通过偶尔发生的非选型交配与杂交个体育性得以维持，但这两种机制会受到两方面因素的制衡：一是幼体杂交个体的表观存活率更低，二是基于生境的偏好或选择——既限制了异种交配，又促进了回交至适应特定生境基因型的过程。该研究系统为揭示急剧资源梯度在生殖隔离中的作用，以及基因渐渗的潜在机制，提供了一个全新的研究范例。